1. Field of the Invention
The present invention generally relates to a centrifugal pellet dryer and more specifically to a self-cleaning dryer and method for removing surface moisture from pelletized product discharged from an underwater pelletizer as a slurry of pellets and water.
2. Description of the Prior Art
Underwater pelletizers which produce a pelletized product in the form of a slurry of pellets and water are well known in the pelletizing industry and in many patents including U.S. Pat. No. 5,059,103 issued Oct. 22, 1991. Centrifugal pellet dryers are also well known and disclosed in various patents including U.S. Pat. No. 6,237,244 issued May 29, 2001. Both of the cited patents are owned by Gala Industries, Inc. (hereinafter “Gala”), the assignee of this application. Additionally, prior patents exist which disclose various structures for drying pellets as illustrated in the following U.S. Pat. Nos. 4,476,019; 4,570,359; 5,187,880; 5,505,537; 5,611,150; 5,638,606; and 5,987,769.
The centrifugal pellet dryers in the prior art satisfactorily dry pellets when properly operated. However, existing pellet dryers have areas in which the pellets being dried become lodged or accumulate. These areas are generally known as hang-up points in which pellets remain after a drying cycle has been completed. The pellets lodged in various hang-up points do not present a problem as long as the same pellet slurry is supplied to the dryer.
However, in many instances, a centrifugal pellet dryer is used to dry different pellets during sequential drying cycles. When a subsequent drying cycle is drying pellets different from the pellets in a previous drying cycle, some of the pellets of the previous drying cycle that have been lodged in the hang-up points will be entrained in and mixed with different pellets being dried in a subsequent drying cycle. This circumstance results in contamination of the pellets being dried in the subsequent drying cycle with pellets that remained in the hang-up points during a previous drying cycle.
The present invention is a self-cleaning dryer and method which overcomes the problems of hang-up points in prior dryers by eliminating the dried pellets from the hang-up points. Thus, contamination of pellets being dried in a drying cycle by pellets left over in various hang-up points during a previous drying cycle in which different pellets were dried is avoided.